Use of formation heat from in situ combustion



May 12, 1964 L w MARX ETAL 3,132,692

USE 0F' FORMATION HEAT FROM IN SITU COMBUSTION Filed July 27, 1959 OOO OOOO

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INVENTOR. ,o J.w. MARX A. D. REICHLE F/G.2 BY@ Z M United States Patent O F 3,132,692 USE OF FORMATION HEAT FROM IN SITU COMBUSTION .lohn W. Marx and Alfred D. Reiehie, Bartlesville, Okla.,

assignors to Phillips Petroleum Company, a corporation of Delaware Filed July 27, 19,59, Ser. No. 829,883 16 Claims. (Cl. 16o- 11) This invention relates to a method of producing a carbonaceous stratum which utilizes the formation heat from in situ combustion of a portion of the stratum.

In situ combustion in the recovery of hydrocarbons from underground strata containing carbonaceous material is becoming more prevalent in the petroleum industry. In this technique of production, combustion is initiated in the carbonaceous stratum and the resulting combustion zone is caused to move thru the stratum by either inverse or direct air drive whereby the heat of combustion of a substantial proportion of the hydrocarbon in the stratum drives out and usually upgrades a substantial proportion of the unburned hydrocarbon material.

The ignition of carbonaceous material in a stratum around a borehole therein followed by injection of air thru the ignition boreholeand recovery of product hydrocarbons and combustion gas thru another borehole inin advance of the combustion zone which prevents mve` ment of air to the combustion process. To overcome this diiiiculty and to permit the continued progress of the combustion zone thru the stratum, inverse air injection has been resorted to. By this technique, a combustion zone is established around an ignition borehole by any suitable means and air is fed thru the stratum to the combustion zone from one or more surrounding boreholes.

In situ combustion techniques are being applied to tar sands, shale, Athabasca sand and other strata in virgin state, to coal veins by fracturing, and to strata partially depleted by primary and even secondary and tertiary recovery methods.

Because of the massive air requirements and the cost of compressor equipment involved, commercial scale in situ combustion of a large field to produce hydrocarbons therefrom must be carried out by burning over long and relatively narrow strips if the operation is to be economically attractive. Adjacent strips must be separated by substantial lanes or strips of unburned stratum in order to prevent catastrophic losses of injected air to the burned out stratum and bypassing of injected air around the unburned stratum thru the burned out stratum from injection wells to production wells. By leaving unburned, intervening lanes or strips between the narrow strips produced by in situ combustion, loss of injected air and bypassing thereof around the stratum to be produced are avoided but some method of producing these lanes or strips must be found in order to recover the oil there-` from. This invention is concerned with a process for re-` covering hydrocarbons from a carbonaceous stratum by burning same in long narrow blocks or strips separated by unburned lanes and producing the unburned lanes or 3,132,692 Patented May v12, 1964 AICC?.

strips between produced blocks or strips of the iield by in situ combustion.

Accordingly, it is an object of the invention to provide a process for producing an oil field or other carbonaceous deposit of a permeable and combustible nature in strips or lanes which can be produced by a reasonable amount of compressor equipment. Another object is to utilize the formation heat produced by in situ combustion in the production of unburned pay zone or stratum. A further object is to provide a process for producing a eld in relatively narrow strips requiring modest compression facilities and equipment which produces the entire iield without leaving unproduced strips or areas.

in the art upon consideration of the accompanying disclosure.

A broad aspect ofthe invention comprises producing spaced-apart blocks of a permeable combustible carbonaceous stratum by in situ combustion so as to leave the range of about 1000 to 1600 or 1700 F. and allow-- ing heat from the produced blocks of stratum to pass into and heat the intervening section to a temperature of at least 150 F., and preferably at least 200 F., and while at said temperature, injecting a warm flushing liuid into the intervening section, preferably along a line midway between the produced blocks, so as to drive iiuid, hydrocarbons from the intervening section into wells in:

each of the adjacent blocks, and recovering the produced hydrocarbons from said wells.

stratum may be produced by either direct or inverse in situ combustion, depending upon the nature of thev stratum. Many strata are not amenable to production by direct Yinjection of combustion-supporting gas but in the event a given eld is amenable to direct drive of a combustion front without plugging,

this technique may be utilized. i

In another embodiment of the invention, the intervening section of stratum between the produced strips is furflushing iiuid. The intervening section containing residual hydrocarbon material is then produced by any one of several methods of in situ combustion. One method comprises igniting the stratum around the injection wells to form a combustion front in a line across these wells,.

- and thereafter injecting combustion-supporting gas either thru the injection wells to advance the combustion front by direct drive to each nearest line of wells in the adjacent strips, or by injecting the combustion-supportingigas thru the nearest lines of wells in the adjacent strips so as to move the front inversely to the injected gas.

A more complete understanding of the invention mayA be had by reference to the accompanying schematic drawing of which FIGURE l is a plan view illustrating a well,

pattern in accordance with a preferred embodiment of the invention, and FIGURE 2 is a plan view of a second type of well pattern useful in producing a stratum in accordr ance with the invention.

Referring to FIGURE 1, a section of afield 10 comprises a burned-over strip 12 and a burned-over strip 14 separated by an unburned strip 16. Strip 12 contains in-;

line rows of wells A, B, C, D, E, F, G, H, and I, each Other ob-l jects of the invention will become apparent to one skilled The'strips or blocks of row containing several wells numbered 1 to 5; and strip 14 contains in-line rows of wells I, K, L, M, N, O, P, Q, and R, each row containing several wells numbered 1 to 5. A row of in-line injection wells S is positioned down the center of intervening strip or section 16. The edges of the burned-out zone adjacent the unburned strip are designated by numerals 18 and 20.

In producing either strip 12 or strip 14, a tire front is established along a line of wells in the strip to be produced by in situ combustion and the resulting iire front is moved thru the field either by inverse or direct injection of combustion-supporting gas to the front. As stated hereinbefore, it is practical and economical to produce in a relatively narrow strip because of compressor requirements. Hence, an economical and practical method comprises igniting the stratum around alternate wells in Vrow E such as around wells 2 and 4 and thereafter injecting air or other combustion-supporting gas thru wells 1, 3, and so as to move the combustion front completely across the line of wells. When this has been accomplished, combustion-supporting gas is then injected thru the wells in rows D and F so as to move combustion fronts in both directions from the line of wells E toward the injection Wells. When the combustion front has arrived adjacent wells in rows D and F, these wells are shut in and injection of combustion supporting gas is commenced in the wells in rows C and F to continue the combustion and move the combustion front to these lines of wells. When the combustion fronts arrive adjacent these rows of wells, the wells therein are also shut in and the next line of wells in the path of the combustion front, in each instance, is utilized as a line of injection wells and the process is continued until the combustion fronts are moved outwardly from the initial ignition wells as far as desired or to the edge of the field.

Strip 14 is preferably produced simultaneously with strip 12 by similar procedure, although it may be produced after producing strip 10. During production of both strips, which may require from one to several years, the temperature of the burned out stratum within the boundary of the strip reaches the range of about 900 to 1600 or 1700 F. (usually at least 1200 F.) and during this period of in situ combustion, heat is traveling by conduction 4into and thru the stratum of the intervening section 16. When the temperature of the stratum along the row of wells S reaches at least 150 F. and preferably at least 200 F., hydrocarbon material in section 16 of the stratum is sufficiently iluidized that a substantial portion of the hydrocarbon material therein can be readily produced by injecting a warm or hot flushing fluid into the stratum thru the wells in row S so as to drive the mobile hydrocarbons therein to the number 5 wells in strip 12 and the number 1 wells in strip 14 which are now utilized as production wells for recovery of flushed hydrocarbons from section 16. Warm or hot combustion gas from any suitable source, steam, hot water, or normally gaseous hydrocarbons may be utilized as the ushing uid. Air may also be utilized as the iiushing iiuid in which case the injected air serves as combustion air whenA it reaches the hotter area of the stratum around the edge of the burned out strips 12 and 14. UponV initiation of combustion along the margins 1S and 20 by the injected air the combustion fronts thus re-established are moved thru section 16 inversely to the injected air and upon continued injection of combustion supporting air the fronts arrive at the line of wells S. If the stratum adjacent wells 5 in strip 12 and wells 1 in strip 14 is below combustion-supporting temperature at the end of the ushing step, ignition may be effected by heating the stratum around these wells to combustion supporting temperature (about 500 F.) and injecting a mixture of air and fuel gas (l to 4 volume percent fuel gas) thru the stratum to the hot area from the S wells.

Another method of producing the residual hydrocarbon material left in section 16 after the flushing step cornd prises initiating combustion along row of wells S in the same manner as combustion `was initiated along the row of Wells E and, thereafter, either injecting combustionsupporting gas thru the wells in row S or thru the line of number 5 wells in strip 12 or the line of number ll Wells in strip 14.

In the event combustion-supporting gas is injected thru the wells in row S, the combustion fronts are driven by direct drive to the nearest line of wells in strips 12 and 14, whereas injection thru the nearest line of wells in these strips causes the combustion frontsto move toward the injection wells inversely to the flow of combustion supporting gas.

After production of the sections of stratum shown in FIGURE l in the manner thus far described, another strip beyond strip 12 or strip iliin unproduced stratum and spaced from the nearest produced strip a distance up to 300 to 500 feet is` produced by in situ combustion and the intervening `section is thereby heated to the range of 150 to 300 or 400 F. so that it may be produced by "flushing and then by in situ combustion by the same methods as applied to section 16. This technique may be continued until the entire held is produced, utilizing a reasonable amount of compressor capacity and production equipment. Y

Referring to FEGURE 2, a well pattern in stratum 10 comprises a central well 30 surrounded by successive rings of wells 40, S0, 60, 70 and 80. Other rings of wells radially outside of those shown will be utilized in the production technique to be described. The section of stratum between central well 30 and ring of wells 50 is produced by initiating combustion around well 30 and moving the resulting combustion front radially outwardly to ring of wellsI 40 by injecting combustion-supporting gas thru these wells until the combustion front arrives and then closing these Wells in and injecting combustion-supporting gas thru ring of wells so as to advance the combustion front to this ring. Simultaneously or sequentially combustion is initiated between the wells` in ring 80 so as to form a combustion front along this ring of wells and the resulting front is advanced thru the stratum toward the wells in ring '70 or the combustion front may be established along the ring of wells 70 and advanced to the ring of wells 80 bythe reverse procedure. The combustion front may be advanced to an outer ring of wells (not shown) by injection of air therethru upon arrival of the combustion front at wells 80 and shutting these wells in. In this manner the stratum between ring of wells 50 and central well 30 and between wells in ring 70 and the wells in ring 80 is heated to the range of 1000 to 1600 or 1700 F., leaving an unburned annular section between rings 50 and 70, and after a waiting period, ifnecessary, the temperature of the stratum along the ring of Wells 60 reaches the 150 or 200 F. level or above. The flushing step is then applied to this intervening an nular section of stratum by injecting flushing iluid thru wells 60 and producing thru wells 50 and 70 in similar manner to the flushing step in the pattern of FIGURE l. The annular flushed out section of stratum may then be produced by in situ combustion in a similarh-n-anner to the production of section 16 in FIGURE 1.

Because of the large number of wells in the rings as the distance from central well 30 increases, it would require described in connection with the pattern of FIGURE 2.

The heating of the unburned stratum intermediate the VIn pushing the melted tar thru relatively high temperature rock around theproduction wells in the burned out strips, sufficient viscosity breaking occurs to keep the product mobile when it cools and to upgrade the same. If additional viscosity reduction is desired, it can be accomplished by adding a small quantity of original counterllow-combustion-product oil from other well patterns in the field, or some other solvent, right at the hot production well heads. Alternatively, additional viscosity breaking may be effected by installing heaters at the production wells and subjecting the produced hydrocarbon material to sufficient heating to upgrade the same to the desired level. However, this additional viscosity breaking by heating will not be required in most applications of the invention.

The strip pattern shown in FIGURE 1 is not essential to the application of this process. A counterflow combustion front can equally well be established by in-line drive along any single row of wells, with displacing fluid injection started in off-set rows of wells as soon as thermal conduction from the combustion zone has sufficiently melted the tar in the region between well rows.

The times required to melt the tar within a commercially practical distance, as calculated from classical heat theory using field values of the thermal diffusivity of a typical bituminous sand (from Bellamy, Missouri) with tar plus residual water in place, are reasonably short. For example, if the edge of burned-over region were initially at 1500 F., and if the original reservoir temperature were 50 F., a temperature of 200 F. could be attained by thermal conduction along a line parallel to and 100 feet from the burn-over edge within 1.1 years. At a 20D-foot distance, about 4.4 years would be required.

Since typical commercial development plans call for something of the order of 2.5 years to burn out one of the combustion strips shown on the figure, it appears that the tar within a 40C-foot separating lane would be substantially melted and capable of being displaced by eX- haust gas injection by the time the two flanking strips are burned out.

As an alternative procedure, proper correlation between barrier lane width and combustion strip burn-out periods can permit oil production from the barrier region into the edge wells of the first burned-out zone, under gas or air drive from the second zone, while combustion is in progress, without requiring that new injection wells be drilled. However, this would have to be most critically timed, in order that the barrier lane continue to serve its function of confining injected air within a combustion zone.

Certain modifications of the invention will become apparent to those skilled in the art and the illustrative details disclosed are not to be construed as imposing unnecessary limitations on the invention.

We claim:

1. A process for producing a permeable combustible carbonaceous stratum which comprises producing a pair of closely laterally spaced-apart blocks of said stratum by in situ combustion thru a line of injection wells and a line of production wells spaced from said line of injection wells in each block by igniting said stratum around one of said line of injection wells and said line of production wells and passing air to the resulting combustion zones so as to move said zones to the other of said line of injection wells and line of production wells, thereby burning completely across each said block and leaving a section intermediate said blocks unburned whereby said blocks are heated to elevated temperatures of at least 1000 F.; allowing heat to pass from said blocks to said section to heat same to a temperature substantially above normal stratum temperature; while at said temperature, injecting 4a flushing fluid into an intermediate portion of said section thru'wells therein so as to drive fluid hydrocarbons therefrom into wells in each of said blocks; and recovering hydrocarbons produced by the in :situ cornbustion vand the flushing steps from said wells.

2.V The process of claim 1 wherein said blocks are parallel, generally rectangular, strips spaced apart a distance in the range of about 50 to 600 feet and said flushing fluid is injected thru a line of injection wells along the center of said intermediate section. j

3. The process of claim 2 further comprising igniting in-place hydrocarbons in said intermediate section along the line of injection wells after the flushing step; and moving the resulting combustion front thru said section to Wells in each of said strips.

4. The process of claim 3 wherein said combustion front is moved thru said section by injecting combustionsupporting gas thru said section from said wells in each strip and produced hydrocarbons are recovered thru the wells in said section. j

5. The process of claim 3 wherein said combustion front is moved thru said section by injecting combustionsupporting gas thru the Wells in said section and produced hydrocarbons are recovered thru wells in each said strip.

6. The process of claim 1 wherein said blocks surround a central well, said intermediate section is an annulus, said flushing fluid is injected thru a ring of wells along the median of said annulus, and' fluid hydrocarbons flushed from said annulus are recovered from rings of wells in said blocks adjacent said annulus.

7. The process of claim 6 further comprising igniting in-place hydrocarbons in said annulus between the wells therein after the flushing step to form a ring-type combustion front; and moving the resulting combustion front thru said section to a ring of wells in each of said blocks by passing air thereto.

8. The process of claim 7 wherein said combustion front is moved thru said section by injecting combustionsupporting gas thru said 'stratum to said front from a ring of wells in each of said blocks and production is recovered thru the wells in said section.

`9. The process of claim 7 wherein said combustion front is moved thru said stratum by injecting combustionsupporting gas thru the wells in said section and production is recovered thru a ring of wells in each of said block.

10. The process of claim 1 wherein said flushing fluid comprises combustion gases.

11. The process of claim 1 wherein said flushing fluid comprises steam.

12. The process of claim 1 wherein said flushing fluid comprises hot water.

13. The process of claim 1 wherein said flushing fluid comprises air.

14. The process of claim 1 wherein combustionsupporting gas is injected thru wells in said section as the flushing fluid and the injected gas ignites said stratum adjacent each said block; and continued injection of said gas moves the resulting combustion front toward the injection wells.

15. A process for producing a permeable combustible carbonaceous stratum which comprises producing a first block of said stratum by igniting said stratum adjacent a line of ignition wells therein and feeding air to the resulting combustion zones so as to move said zones thru said stratum to a line of offset wells within said first block and produce hydrocarbons thru one of the line of wells whereby said first block is heated to a temperature of at least 1000 F.; producing a second block of said stratum laterally spaced from said first block by a technique similar to that applied to said first block so as to produce hydrocarbons thru wells in said second block, heat said second blockl to a temperature of at least 1000 F., and leave a section of said stratum adjacent and intermediate said blocks unburned; recovering the hydrocarbons produced by the combustion steps in said blocks; allowing heat from said `blocks to invade and heat saidsection to @temperature substantially above normal stratum tem'- perature; While at said temperature, passing a ushing fluid between a line of wells in said section and a line of Wells in at leasty one of said blocks; `and recovering hydrocarbons from one of said lines of wells.

16. The process of claim 15 further comprising igniting in-place hydrocarbons in said intermediate section after the flushing step, and moving a resulting combustion zone thru said section bypassing combustion supporting gas to said zone; and recovering hydrocarbons produced thereby from wells in one of said blocks and said intermediate section.

UNITED STATES PATENTS Heilman et'al; Sept. 20, 1955 Elkins Feb. 14, 1956 Pelzer Apr. 9, 1957 Parker June 2, 1959 Crawiord Aug. 11, 1959 Hennig Sept. 29, 1959 Heilman et a1 Feb. 9, 1960 Dew et al Sept. 27, 1960 Wyllie Oct. 9, 1962 

1. A PROCESS FOR PRODUCING A PERMEABLE COMBUSTIBLE CARBONACEOUS STRATUM WHICH COMPRISES PRODUCING A PAIR OF CLOSELY LATERALLY SPACED-APART BLOCKD OF SAID STRATUM BY IN SITU COMBUSTION THRU A LINE OF INJECTION WELLS AND A LINE OF PRODUCTION WELLS SPACED FROM SAID LINE OF INJECTION WELLS IN EACH BLOCK BY IGNITING SAID STRATUM AROUND ONE OF SAID LINE OF INJECTION WELLS AND SAID LINE OF PRODUCTION WELLS AND PASSING AIR TO THE RESULTING COMBUSTION ZONES SO AS TO MOVE SAID ZONES TO THE OTHER OF SAID LINE OF INJECTION WELLS AND LINE OF PRODUCTION WELLS, THEREBY BURNING COMPLETELY ACROSS EACH SAID BLOCK AND LEAVING A SECTION INTERMEDIATE SAID BLOCKS UNBURNED WHEREBY SAID BLOCKS ARE HEATED TO ELEVATED TEMPERATURES OF AT LEAST 1000*F.; ALLOWING HEAT TO PASS FROM SAID BLOCKS TO SAID SECTION TO HEAT SAME TO A TEMPERATURE SUBSTANTIALLY ABOVE NORMAL STRATUM TEMPRATURE; WHILE AT SAID TEMPERATURE, INJECTING A FLUSHING FLUID INTO AN INTERMEDIATE PORTION OF SAID SECTION THRU WELLS THEREIN SO AS TO DRIVE FLUID HYDROCARBONS THEREFROM INTO WELLS IN EACH OF SAID BLOCKS; AND RECOVERING HYDROCARBONS PRODUCED BY THE IN SITU COMBUSTION AND THE FLUSHING STEPS FROM SAID WELLS. 